netdev - Re: [PATCH 2/3] net: Add net device irq siloing feature

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Message-ID: <20110416014547.GA2200@neilslaptop.think-freely.org>
Date:	Fri, 15 Apr 2011 21:49:03 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Dimitris Michailidis <dm@...lsio.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH 2/3] net: Add net device irq siloing feature

On Fri, Apr 15, 2011 at 11:49:03PM +0100, Ben Hutchings wrote:
> On Fri, 2011-04-15 at 16:17 -0400, Neil Horman wrote:
> > Using the irq affinity infrastrucuture, we can now allow net devices to call
> > request_irq using a new wrapper function (request_net_irq), which will attach a
> > common affinty_update handler to each requested irq.  This affinty update
> > mechanism correlates each tracked irq to the flow(s) that said irq processes
> > most frequently.  The highest traffic flow is noted, marked and exported to user
> > space via the affinity_hint proc file for each irq. In this way, utilities like
> > irqbalance are able to determine  which cpu is recieving the most data from each
> > rx queue on a given NIC, and set irq affinity accordingly.
> [...]
> 
> Is irqbalance expected to poll the affinity hints?  How often?
> 
Yes, its done just that for quite some time.  Intel added that ability at the
same time they added the affinity_hint proc file.  Irqbalance polls the
affinity_hint file at the same time it rebalances all irqs (every 10 seconds).
If the affinity_hint is non-zero, irqbalance just copies it to smp_affinity for
the same irq.  Up until now thats been just about dead code because only ixgbe
sets affinity_hint.  Thats why I added the affinity_alg file, so irqbalance
could do something more intellegent than just a blind copy.  With the patch that
I referenced I added code to irqbalance to allow it to preform different
balancing methods based on the output of affinity_alg.
Neil

> Ben.
> 
> -- 
> Ben Hutchings, Senior Software Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
> 
> 
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